1. Field of the Invention
This invention relates to positioning devices, and in particular, to a device for positioning and varying the distance between a sensor element and a rotor shaft of a turbine apparatus.
Description of the Prior Art
In a large axial flow turbine apparatus, a rotor shaft is rotatably supported at each end thereof in a thrust bearing device. The rotor shaft has a plurality of arrays of rotating blades disposed thereon, each array of rotating blades being disposed a predetermined axial distance from a corresponding array of stationary blades mounted within the turbine casing. For maximum efficiency of the turbine, the rotating and stationary blades are spaced precise axial distances apart. Any axial displacement of the rotor shaft would obviously cause abrasion between the rotating and stationary blades.
For this reason, it is advantageous to know whether or not forces on the rotor member are sufficient to axially displace the rotor with respect to the turbine casing.
In order to dectect whether such axial displacement of the rotor has occurred, the present art disposes a position sensor device a predetermined distance away from a disc member which is mounted on the rotor. The sensing device is mounted on and remains stationary with respect to the turbine casing. Since it is possible for axial displacement of the rotor to occur in certain regions of the turbine, for example, due to thermal expansion of the rotor, the position sensor is disposed within the turbine casing at a point adjacent the thrust bearing. It is disposed at this position where very little axial displacement of the rotor occurs.
The sensor element is capable of both sensing position shifts between it and the rotor and also initiating an associated emergency trip system. Thus, if the position sensor detects a change in the distance between the rotor disc and the position sensor, the emergency trip system will be activated. Activation of the emergency trip system will cut off the supply of elastic fluid through the turbine apparatus and preclude the possibility of the turbine destroying itself due to an excessive axial displacement of the rotor shaft.
At present, only the emergency trip initiation function of the position sensor is testable. There is no arrangement presently available to test whether or not the distance detection function of the sensor is operable.
It is apparent that a device which will permit adjusting the predetermined distance between the sensor element and the rotor disc in order to examine the ability of the sensor to detect axial deflections of the rotor is most advantageous. It is thus seen that the ability to test whether the distance-sensing capabilities of the sensor are operable, in addition to testing the trip initiation capabilities, provides for greater reliability to users of the turbine system embodying the present invention.
Such a positioning device for the sensor element can be utilized to facilitate periodic testing of the rotor emergency trip mechanism. In addition, a device which would change the distances between the position sensor and the rotor disc accurately and under control of an automatic control system, such as a computer, would be clearly superior to any manually operated positioning arrangement. Also, a device which, after measuring the ability of the sensor element to ascertain varying distances between it and a rotor, would return the sensor element to a predetermined normal position is desirable.